Dramatic drop in velocity with exact same components - strange! Ever seen this??

[nimrod_gn]

I have a Browning X-Bolt in 28 Nosler I've been shooting for a couple of years with 143 gr Hammer Hunters. I recently got my hands on some ADG brass and N570 powder. I've been wanting to try some load workup with these new components. Went to the range a week ago to do pressure test and it went like this:

83 grains - 3465 fps with no pressures signs
84 grains - 3575 fps with no pressure signs
85 grains - 3600 fps with no pressure signs
86 grains - 3722 fps with slight ejector mark, no sticky bolt

Decided to focus around the 86 grain level (+/- .3 grains) to test accuracy.

Back at the range yesterday to try those loads and they shot .5 MOA BUT they all ran velocity around 3500 fps instead of around 3700.

I've been loading for 35 years and never seen anything like this. Components were exactly the same each time:

New ADG brass
N570 powder
CCI-250 primer
143 grain Hammer Hunter bullet

using Magnetospeed chrono

Anybody experienced anything like this?? It's driving me crazy trying to figure out why velocity would drop 200 fps with exact same components, seating depth, etc.

 

[Dosh]

On the first trip were the loads in new brass and second trip once fired?

 

[ButterBean]

On the first trip were the loads in new brass and second trip once fired?

^^^^^^^^^^^^^^ This We Need To Know ^^^^^^^^^^^^^^^^^

 

[nimrod_gn]

^^^^^^^^^^^^^^ This We Need To Know ^^^^^^^^^^^^^^^^^

ALL loads were with brand new, never fired brass. Sorry, I should have mentioned that

 

[ButterBean]

ALL loads were with brand new, never fired brass. Sorry, I should have mentioned that

Copy. Before you go crazy just load another batch and verify

 

[P7M13]

Curiosity question -- what prompted you to focus on the 86 grains?
84 and 85 grains, being close velocities suggest you have a node somewhere in there.
Agree with Bean, shoot another course.
I expect your virgin ADG is all the same batch, and would anticipate consistency in your loaded rounds.

 

[nimrod_gn]

Curiosity question -- what prompted you to focus on the 86 grains?
84 and 85 grains, being close velocities suggest you have a node somewhere in there.
Agree with Bean, shoot another course.
I expect your virgin ADG is all the same batch, and would anticipate consistency in your loaded rounds.

I agree. I saw there was likely a node in that range but my experience with Hammers is they seem to like near maximum. That's why I started to work around the 86 area. I guess this may remain a mystery. I'll just do another work up/pressure test and see what happens this time.

 

[ButterBean]

I agree. I saw there was likely a node in that range but my experience with Hammers is they seem to like near maximum. That's why I started to work around the 86 area. I guess this may remain a mystery. I'll just do another work up/pressure test and see what happens this time.

Let's see what happens first and then we'll go from there

 

[Dmagna]

How many rounds down the barrel?

 

[nimrod_gn]

How many rounds down the barrel?

200ish

 

[kb1035]

I have experienced this exact scenario in my Rem. 700 30-06. Same brass, same powder (from same exact cannister), same bullets (from same box), same charge. No significant ambient temperature differences either. Yet, a proven load showed 175-200 fps velocity loss and decreased accuracy/consistency. After this aberration, I tested the load on two later occasions and it returned to normal form.

The only thing I could come up with was maybe an unknown chronograph, powder scale, or similar issue. It still puzzles me to this day.

Good luck on the mystery.

 

[nimrod_gn]

I have experienced this exact scenario in my Rem. 700 30-06. Same brass, same powder (from same exact cannister), same bullets (from same box), same charge. No significant ambient temperature differences either. Yet, a proven load showed 175-200 fps velocity loss and decreased accuracy/consistency. After this aberration, I tested the load on two later occasions and it returned to normal form.

The only thing I could come up with was maybe an unknown chronograph, powder scale, or similar issue. It still puzzles me to this day.

Good luck on the mystery.

A buddy and I have been racking our brains trying to figure out why, thinking through anything that could have changed. Since components and even temperature were all the same, our only thoughts were similar - powder scale or chronograph. I haven't seen any similar issues with other rifles/loads using same powder scale so maybe my chronograph was wacko one day? What's interesting though is the first day the 86 gr load showed some minor ejector mark but 86 gr loads since haven't. Hmmmm

 

[Bob Wright]

"86 gr load showed some minor ejector mark but 86 gr loads since haven't. Hmmmm"

Agree, reload same. Above remark by OP, cleaned barrel by chance prior to last 86 gr load?

 

[B-LOT Banga]

Did you clean your barrel or left it as is from the trip before?